1. Field of the Invention
The present invention relates to an endoscope whose insertion portion is rotatable in a direction around a central axis thereof with respect to an operation portion.
2. Description of the Related Art
In an insertion portion of an endoscope, a bending portion is used which is operated to bend in four vertical and horizontal directions, but a bending portion is also used which is operated to only bend in two directions in order to simplify a bending mechanism for a smaller diameter of the insertion portion. In such a two-way bending endoscope, the insertion portion is rotated halfway in a direction around a central axis thereof to achieve vertical and horizontal bending.
In an endoscope in Jpn. Pat. Appln. KOKAI Publication No. 7-345, an insertion portion can be switched among the following states: a state where the insertion portion is rotatable with respect to an operation portion; a state where the insertion portion is provided with predetermined force urging to rotate with respect to the operation portion; and a state where the insertion portion is fixed with respect to the operation portion. In the state where the insertion portion is provided with the predetermined force urging to rotate, the insertion portion can be rotated by providing a force equal to or greater than the force urging to rotate and the insertion portion can be automatically returned to an original state by releasing this force.
In an endoscope in Jpn. Pat. Appln. KOKAI Publication No. 2004-305413, an insertion portion connecter at a proximal end of an insertion portion is internally fitted into an operation portion connecter at a distal end of an operation portion rotatably in a direction around an axis thereof. On an inner peripheral surface of the operation portion connecter and an outer peripheral surface of the insertion portion connecter, there are formed tapered surfaces which are pressed slidably on each other and which increase in diameter toward a distal side. Between these tapered surfaces, there is interposed an O-ring as a frictional force generating member, so that the insertion portion is not rotated with respect to the operation portion by a force equal to or less than the given force.
In an endoscope in the specification of U.S. Pat. No. 6,749,572, a rotation control wheel externally fitted onto and fixed to a proximal end of an insertion portion can be rotationally operated to rotate the insertion portion. Then, a brake handle disposed at a distal end of an operation portion is rotationally driven to linearly drive a brake member so that the brake member is pressed on the rotation control wheel, and thus the rotation control wheel is fixed to the brake member, thereby making it possible to fix the insertion portion to the operation portion.